Node Device, Node System, and Method and Program for Changing Statistic Information Management Table Used for the Node Device

1. A node apparatus for observing communication quality of a network, comprising: packet observer for observing packets flowing through the network; packet classifying unit for looking up a specific field in a packet observed by said packet observer, and classifying said packet in accordance with a type of said field; monitoring importance degree calculator for calculating a monitoring importance degree for each type of packets classified by said packet classifying unit; and statistic information manager provided with a statistic information management table for managing statistic information on communication quality of a network, for searching said statistic information, and in a case that said statistic information has been created, updating said statistic information, or in a case that said statistic information has not been created, deciding whether swapping should occur in said statistic information management table based on said monitoring importance degree.

2. A node apparatus according to claim 1 , wherein said packet observer uses part of packets passing through said network as a target of observation.

3. A node apparatus according to claim 1 , wherein said monitoring importance degree calculator calculates the ratio or number of arrivals of a class based on a history of packets that arrived in the past, and calculates said monitoring importance degree based on a result of the calculation.

4. A node apparatus according to claim 1 , wherein said monitoring importance degree calculator comprises a table in which a history of packets that arrived in the past is stored, and calculates the ratio or number of arrivals of said class of packets by searching for the presence of said class of packets in said history of packets.

5. A node apparatus according to claim 1 , wherein said monitoring importance degree calculator comprises a table in which a history of packets that arrived in the past is stored and which contains as its entry a flow ID for registering an identifier of a flow, and a number of times of updating or looking up of the entry.

6. A node apparatus according to claim 1 , wherein said statistic information manager has either one of the counter value or monitoring importance degree as one piece of entry information in said statistic information management table, and in a case that a packet that has arrived is found in said statistic information management table, updates statistic information for a corresponding class, or in a case that the packet is not found in said statistic information management table, newly registers the packet that has arrived based on the counter value or monitoring importance degree in said entry information, and dislodges a registered entry information from the table.

7. A node apparatus according to claim 1 , wherein, when a class of a packet that has arrived is not found in said statistic information management table, said statistic information manager selects an entry in said statistic information table, and determines a swapping probability for the entry based on the monitoring importance degree written in the entry.

8. A method of swapping in a statistic information management table for use in a node apparatus for observing communication quality of a network, comprising: a packet observing step of observing packets flowing through the network; a packet classifying step of looking up a specific field in a packet observed by said packet observing processing, and classifying said packet in accordance with a type of said field; a monitoring importance degree calculating step of calculating a monitoring importance degree for each type of packets classified by said packet classifying processing; and a statistic information managing step of providing a statistic information management table for managing statistic information on communication quality of a network, searching said statistic information, and in a case that said statistic information has been created, updating said statistic information, or in a case that said statistic information has not been created, deciding whether swapping should occur in the statistic information management table based on said monitoring importance degree.

9. A method of swapping in a statistic information management table according to claim 8 , wherein said packet observing step uses part of packets passing through said network as a target of observation.

10. A method of swapping in a statistic information management table according to claim 8 , wherein said monitoring importance degree calculating step comprises calculating the ratio or number of arrivals of a class based on a history of packets that arrived in the past, and calculating said monitoring importance degree based on a result of the calculation.

11. A method of swapping in a statistic information management table according to claim 8 , wherein said monitoring importance degree calculating step is configured to comprise a table in which a history of packets that arrived in the past is stored, and calculate the ratio or number of arrivals of said class of packets by searching for the presence of said class of packets in said history of packets.

12. A method of swapping in a statistic information management table according to claim 8 , wherein said monitoring importance degree calculating step comprises a table in which a history of packets that arrived in the past is stored and which contains as its entry a flow ID for registering an identifier of a flow, and a number of times of updating or looking up of the entry.

13. A method of swapping in a statistic information management table according to claim 8 , wherein said statistic information managing step has either one of the counter value or monitoring importance degree as one piece of entry information in said statistic information management table, and in a case that a packet that has arrived is found in said statistic information management table, updates statistic information for a corresponding class, or in a case that the packet is not found in said statistic information management table, newly registers the packet that has arrived based on the counter value or monitoring importance degree in said entry information, and dislodges a registered entry information from the table.

14. A method of swapping in a statistic information management table according to claim 8 , wherein, when a class of a packet that has arrived is not found in said statistic information management table, said statistic information managing step comprises selecting an entry in said statistic information table, and determining a swapping probability for the entry based on the monitoring importance degree written in the entry.

15. A communication system for observing communication quality of a network, comprising: packet observing unit for observing packets flowing through the network; packet classifying unit for looking up a specific field in a packet observed by said packet observing unit, and classifying said packet in accordance with a type of said field; monitoring importance degree calculating unit for calculating a monitoring importance degree for each type of packets classified by said packet classifying unit; and statistic information managing unit provided with a statistic information management table for managing statistic information on communication quality of a network, for searching said statistic information, and in a case that said statistic information has been created, updating said statistic information, or in a case that said statistic information has not been created, deciding whether swapping should occur in said statistic information management table based on said monitoring importance degree.

16. A non-transitory computer readable medium comprising a program for a node apparatus for observing communication quality of a network, wherein said program causes said node apparatus to execute: packet observation processing of observing packets flowing through the network; packet classification processing of looking up a specific field in a packet observed by said packet observation processing, and classifying said packet in accordance with a type of said field; monitoring importance degree calculation processing of calculating a monitoring importance degree for each type of packets classified by said packet classification processing; and statistic information management processing of providing a statistic information management table for managing statistic information on communication quality of a network, searching said statistic information, and in a case that said statistic information has been created, updating said statistic information, or in a case that said statistic information has not been created, deciding whether swapping should occur in the statistic information management table based on said monitoring importance degree.